pack, pcat, unpack - compress and expand files
pack [-f/] [-] file...
unpack [-/] file...
The pack command attempts to store the specified files in a compressed form. Wherever possible (and useful), each input file file is replaced by a packed file file.z with the same access modes, access and modified dates, and owner as those of file. If pack is successful, file is removed.
The amount of compression obtained depends on the size of the input file and the character frequency distribution. Because a decoding tree forms the first part of each .z file, it is usually not worthwhile to pack files smaller than three blocks, unless the character frequency distribution is very skewed, which can occur with printer plots or pictures.
Typically, text files are reduced to 60-75% of their original size. Load modules, which use a larger character set and have a more uniform distribution of characters, show little compression, the packed versions being about 90% of the original size.
The pack utility returns a value that is the number of files that it failed to compress. If that number exceeds 255, 255 is returned.
No packing occurs if:
The last segment of the file name must be short enough to allow space for the appended .zextension. Directories cannot be compressed.
The pcat command does for packed files what cat(1) does for ordinary files, except that pcat cannot be used as a filter. The specified files are unpacked and written to the standard output.
pcat returns the number of files it was unable to unpack. Failure can occur if:
The unpack command expands files created by pack. For each file specified in the command, a search is made for a file called file.z (or just file, if file ends in .z). If this file appears to be a packed file, it is replaced by its expanded version. The new file has the .z suffix stripped from its name, and has the same access modes, access and modification dates, and owner as those of the packed file.
unpack returns a value that is the number of files it was unable to unpack. Failure can occur for the same reasons that it can in pcat, as well as for the following:
The following options are supported by pack:
The following options are supported by pack and unpack:
The following operands are supported:
See largefile(5) for the description of the behavior of pack, pcat, and unpack when encountering files greater than or equal to 2 Gbyte ( 2^31 bytes).
Example 1 Viewing a Packed File
To view a packed file named file.z use:
example% pcat file.z
example% pcat file
Example 2 Making and Unpacked Copy:
To make an unpacked copy, say nnn, of a packed file named file.z (without destroying file.z) use the command:
example% pcat file >nnn
See environ(5) for descriptions of the following environment variables that affect the execution of pack, pcat, and unpack: LC_CTYPE, LC_MESSAGES, and NLSPATH.
The following exit values are returned:
See attributes(5) for descriptions of the following attributes:
cat(1), compress(1), zcat(1), fgetattr(3C), fsetattr(3C)attributes(5), environ(5), largefile(5)
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Created 1996-2023 by Maxim Chirkov
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